RE: [????] Re: [PATCH] RDMA/core: Prevent soft lockup during large user memory region cleanup

["Li,Rongqing" <lirongqing@baidu.com>]

> On Tue, Nov 11, 2025 at 03:01:07PM +0800, lirongqing wrote:
> > From: Li RongQing <lirongqing@baidu.com>
> >
> > When a process exits with numerous large, pinned memory regions
> > consisting of 4KB pages, the cleanup of the memory region through
> > __ib_umem_release() may cause soft lockups. This is because
> > unpin_user_page_range_dirty_lock()
> 
> Do you have soft lookup splat?
> 


A user meet this lockup issue on ubuntu 22.04 kernel, after change watchdog_thresh to 60, the soft lockup is disappeared.

I think his program registered too many memory region(this program has 400G memory), but the lockup should be fixed too.

[9769474.755472] mlx5_core 0000:b0:00.0: mlx5_query_module_eeprom_by_page:475:(pid 3380349): Module ID not recognized: 0x19
[9793445.031306] watchdog: BUG: soft lockup - CPU#44 stuck for 26s! [python3:73464]
[9793445.032792] Kernel panic - not syncing: softlockup: hung tasks
[9793445.033695] CPU: 44 PID: 73464 Comm: python3 Tainted: G           OEL    5.15.0-124-generic #134-Ubuntu
[9793445.035024] Hardware name: BCC, BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[9793445.036500] Call Trace:
[9793445.036955]  <IRQ>
[9793445.037339]  show_stack+0x52/0x5c
[9793445.037892]  dump_stack_lvl+0x4a/0x63
[9793445.038485]  dump_stack+0x10/0x16
[9793445.039024]  panic+0x15c/0x33b
[9793445.039540]  watchdog_timer_fn.cold+0xc/0x16
[9793445.040204]  ? lockup_detector_update_enable+0x60/0x60
[9793445.040999]  __hrtimer_run_queues+0x104/0x230
[9793445.041678]  ? clockevents_program_event+0xaa/0x130
[9793445.042427]  hrtimer_interrupt+0x101/0x220
[9793445.043070]  __sysvec_apic_timer_interrupt+0x5e/0xe0
[9793445.043826]  sysvec_apic_timer_interrupt+0x7b/0x90
[9793445.044563]  </IRQ>
[9793445.044968]  <TASK>
[9793445.045353]  asm_sysvec_apic_timer_interrupt+0x1b/0x20
[9793445.046138] RIP: 0010:free_unref_page+0xff/0x190
[9793445.046861] Code: b9 ae 72 44 89 ea 4c 89 e7 e8 5d ce ff ff 65 48 03 1d fd b8 ae 72 41 f7 c6 00 02 00 00 0f 84 30 ff ff ff fb 66 0f 1f 44 00 00 <5b> 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc ba 00 08 0
0 00 e9 41
[9793445.049506] RSP: 0018:ff7f1fce1bb039a8 EFLAGS: 00000206
[9793445.050315] RAX: 0000000000000000 RBX: ff40b8648212ea88 RCX: ffc2d725bc39b808
[9793445.051371] RDX: ff7f1fce1bb03920 RSI: ffc2d725bc39b7c8 RDI: ff40b86a3ffd7010
[9793445.052436] RBP: ff7f1fce1bb039d0 R08: 0000000000000010 R09: 0000000000000000
[9793445.053498] R10: ffc2d725bc39b800 R11: dead000000000122 R12: ffc2d728f67bcdc0
[9793445.054551] R13: 0000000000000000 R14: 0000000000000297 R15: 0000000000000000
[9793445.055604]  ? free_unref_page+0xe3/0x190
[9793445.056255]  __put_page+0x77/0xe0
[9793445.056831]  put_compound_head+0xed/0x100
[9793445.057504]  unpin_user_page_range_dirty_lock+0xb2/0x180
[9793445.058344]  __ib_umem_release+0x57/0xb0 [ib_core]
[9793445.059148]  ib_umem_release+0x3f/0xd0 [ib_core]
[9793445.059916]  mlx5_ib_dereg_mr+0x2e9/0x440 [mlx5_ib]
[9793445.060716]  ib_dereg_mr_user+0x43/0xb0 [ib_core]
[9793445.061492]  uverbs_free_mr+0x15/0x20 [ib_uverbs]
[9793445.062242]  destroy_hw_idr_uobject+0x21/0x60 [ib_uverbs]
[9793445.063091]  uverbs_destroy_uobject+0x38/0x1b0 [ib_uverbs]
[9793445.063947]  __uverbs_cleanup_ufile+0xd1/0x150 [ib_uverbs]
[9793445.064806]  uverbs_destroy_ufile_hw+0x3f/0x100 [ib_uverbs]
[9793445.065671]  ib_uverbs_close+0x1f/0xb0 [ib_uverbs]
[9793445.066450]  __fput+0x9c/0x280
[9793445.066993]  ____fput+0xe/0x20
[9793445.067541]  task_work_run+0x6a/0xb0
[9793445.068149]  do_exit+0x217/0x3c0
[9793445.068726]  do_group_exit+0x3b/0xb0
[9793445.069327]  get_signal+0x150/0x900
[9793445.069926]  arch_do_signal_or_restart+0xde/0x100
[9793445.070679]  ? fput+0x13/0x20
[9793445.071195]  ? do_epoll_wait+0x8f/0xe0
[9793445.071817]  exit_to_user_mode_loop+0xc4/0x160
[9793445.072526]  exit_to_user_mode_prepare+0xa0/0xb0
[9793445.073253]  syscall_exit_to_user_mode+0x27/0x50
[9793445.073985]  ? x64_sys_call+0xfab/0x1fa0
[9793445.074632]  do_syscall_64+0x63/0xb0
[9793445.075227]  ? exit_to_user_mode_prepare+0x37/0xb0
[9793445.075985]  ? syscall_exit_to_user_mode+0x2c/0x50
[9793445.076739]  ? x64_sys_call+0x1ea1/0x1fa0
[9793445.077394]  ? do_syscall_64+0x63/0xb0
[9793445.078011]  ? syscall_exit_to_user_mode+0x2c/0x50
[9793445.078762]  ? x64_sys_call+0xfab/0x1fa0
[9793445.079404]  ? do_syscall_64+0x63/0xb0
[9793445.080018]  ? x64_sys_call+0x1ea1/0x1fa0
[9793445.080674]  ? do_syscall_64+0x63/0xb0
[9793445.081287]  ? do_syscall_64+0x63/0xb0
[9793445.081903]  ? do_syscall_64+0x63/0xb0



-Li



> > is called in a tight loop for unpin and releasing page without
> > yielding the CPU.
> >
> > Fix the soft lockup by adding cond_resched() calls in
> > __ib_umem_release
> >
> > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> > ---
> >  drivers/infiniband/core/umem.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/infiniband/core/umem.c
> > b/drivers/infiniband/core/umem.c index c5b6863..70c1520 100644
> > --- a/drivers/infiniband/core/umem.c
> > +++ b/drivers/infiniband/core/umem.c
> > @@ -59,6 +59,7 @@ static void __ib_umem_release(struct ib_device *dev,
> struct ib_umem *umem, int d
> >  		unpin_user_page_range_dirty_lock(sg_page(sg),
> >  			DIV_ROUND_UP(sg->length, PAGE_SIZE), make_dirty);
> >
> > +	cond_resched();
> >  	sg_free_append_table(&umem->sgt_append);
> >  }
> >
> > --
> > 2.9.4
> >